Chair base



FIG. 1 is a perspective view of a chair base showing my new design;

FIG. 2 is a front elevational view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a left side elevational view thereof;

FIG. 5 is a right side elevational view thereof;

FIG. 6 is a top plan view thereof;

FIG. 7 is a bottom plan view thereof; and,

FIG. 8 is a perspective view of a chair base with a seat cushion in broken line is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a chair base, as shown and described. 